1. Field of the Invention
The invention relates to a continuously variable transmission, in particular for a motor vehicle, at least provided with a primary pulley with an input pulley shaft, a secondary pulley with an output pulley shaft, a drive belt positioned around the primary and secondary pulleys and a transmission mechanism which is constructed in combination with a direct/neutral/reverse group and is positioned after the secondary pulley and has at least two adjustable transmission ratios for forward drive.
2. Description of the Related Art
A transmission of this type is known and is used in particular for motor vehicles. With a transmission of this type the radial position of the drive belt between the primary and secondary pulleys can be varied, the relationship between the two radial positions of the drive belt in the pulleys determining the transmission ratio. With this arrangement the range of possible transmission ratios is determined by the radial dimension of the pulleys and by the strength and durability of the drive belt. In general as large as possible a range for the transmission ratios is desired when the transmission is used in motor vehicles. To this end a transmission of this type can also be provided with a separate transmission mechanism having at least two adjustable transmission ratios. In this way a transmission range of the drive belt/pulley combination, which in itself is limited because of the limited dimensions thereof, can be increased by combining this with the at least two adjustable transmission ratios of the transmission mechanism. In this way a continuously variable transmission with a relatively large transmission range is obtained in practice.
With this arrangement the transmission mechanism is mounted in the drive direction after the secondary pulley; the adjustable transmission ratio of the transmission mechanism (output revs:input revs) can advantageously be greater than one in order to prevent high drive belt revs, or can advantageously be less than one in order specifically to obtain high drive belt revs. A transmission mechanism of this type is provided with clutches which are adjustable, so that the desired transmission ratio of the transmission mechanism is adjustable.
In practice the said transmission mechanism is frequently constructed in combination with a DNR group (for adjustment of direct, neutral or reverse drive).
Nevertheless, in practice it has been found that, partly as a result of the installation of the requisite hydraulic control circuit, a combination of this type is relatively large, both in the radial and in the axial direction. In particular in the case of motor vehicles with rear wheel drive, this is a disadvantage because only a limited radial installation space is available in such vehicles.